Joining connection, method for producing the same, and a steering column for motor vehicles comprising such a joining connection

ABSTRACT

A joining connection between a circumferentially closed hollow profile and an add-on part which is provided with a passage opening and consists of a material of lower strength than the material of the hollow profile is disclosed. Additionally, a method for producing the connection and to a steering column having this joining connection is disclosed. In order to connect a hollow profile and an add-on part having lower strength than the hollow profile non-releasably to each other in a simple, reproducible and reliable manner, and furthermore in order to reliably fit a holder as an add-on part to the casing tube of the steering column, where the holder has a lower strength than the casing tube, with a low outlay on components and costs and with exact, reproducible positioning of the two joining partners with respect to each other in the joining connection, a recess is provided which is spaced away from the end sides of the add-on part on the inside of the passage opening, to slide the add-on part with its passage opening onto the hollow profile and to jam it to the hollow profile in this sliding-fit position by a local expansion of the hollow profile. The expansion being formed by internal high-pressure deformation at the location of the recess.

BACKGROUND AND SUMMARY OF THE INVENTION

This application claims the priority of German Patent Document 199 29957.9, filed Jun. 29, 1999, and International Application No.PCT/EP00/04895, filed May 30, 2000, the disclosures of which areexpressly incorporated by reference herein.

The invention relates to a joining connection and to a method forproducing the same, and to a steering column of a motor vehicle.

A generic steering column is disclosed in German Patent Document DE 3600 134 C1 whose casing tube, which consists of plastic, has injectionmolded integrally on it a holder for the securing of a steering columnswitch. The outlay on the engineering of the mold is very considerablein this case, since the injection mold has to be of very complex design.Furthermore, because of the stiffness required by the casing tube, theplastic of the casing tube is very brittle and is therefore easilybreakable in the event of a crash, which may mean serious consequencesin terms of health for the vehicle occupants, in particular for thedriver.

In various applications, components which are exactly aligned with oneanother have to be secured on a hollow profile or a tube, the securingbetween the component and tube, i.e., the joining connection, having towithstand axial displacement forces and torsional moments. One possiblejoining technique is the internal high-pressure deformation techniquewhich is used in the production of frictional connections between thecomponent and tube, for example in the case of engineered camshafts. Inthis case, the components to be joined, namely the cam and tube, arefirst positioned with respect to each other and then the tube ispartially acted upon by means of internal high pressure—delivered via anexpansion lance inserted into the tube—below the cam. This resultssuccessively in flowing of the tube material, in expansion and bearingof the tube material against the cam and in the common expansion of thetube material and cam material. The pressure is set in such a mannerthat the cam can spring back elastically after it has been relieved ofpressure. The springing-back together with a simultaneous, permanentincrease in diameter of the tube enables a virtually nonreleasable,frictional joining connection to be achieved. However, a preconditionfor this type of joining connection is that the yield strength of thejoining part, the cam, is greater than the yield strength of the tube.However, if the yield-strength ratios are reversed, the internal highpressure, which acts in an expansive manner, causes the joining part toexplode relatively rapidly.

A generic joining connection and a method for production thereof is alsodisclosed in German Patent Document DE-A-2 400 148, in which a tube isslid through a hole in a tube plate and, after insertion into the tubeof a probe provided with axially spaced sealing rings, is subjected to apressurized liquid via a duct of the probe which first runs axially andthen radially between the sealing rings. The tube is thereby expandedand becomes positioned against the hole wall of the tube plate, in whichcase only the surrounding region of a weld, which has been undertaken onthe end side between the tube and tube plate, remains recessed. In orderto obtain higher withdrawal forces, widened portions lying one behindanother in the hole wall are incorporated, with the result that duringthe hydraulic expansion of the tube a form-fitting connection also comesabout together with—as seen in the axial direction—undercuts whichresult in the tube becoming jammed in the hole of the tube plate. Inthis case, it is disadvantageous that the tube material is first of allpositioned against the hole wall and only then is pressed into thewidened portions, since the premature bearing enables friction to occurbetween the tube and the hole wall, the friction obstructing furtherflow of material into the widened portions. In this connection,depending on the depth of the widened portions, the material can becomethinned at this point to such an extent that the tube may burst and theproduction reliability is thus not ensured as desired. Furthermore, theuse of material for the tube plate is restricted, since, when a materialhaving a lower yield strength than the material of the tube is used,after bearing of the tube against the hole wall the tube plate wouldinevitably break during further expansion into the widened portions.

The present invention is based on the object of finding a joiningconnection and a method for the production thereof, with which a hollowprofile and an add-on part having a lower yield strength than the hollowprofile can be connected non-releasably to each other in a simple,reproducible and reliable manner. Furthermore, a generic steering columnis to be developed in such a manner that a holder can be reliably fittedas an add-on part to the casing tube of the steering column, the holderhaving a lower yield strength than the casing tube, with a low outlay oncomponents and costs and with an exactly reproducible positioning of thetwo joining partners with respect to each other in the joiningconnection.

In accordance with the invention, because of the local expansion of thehollow profile into the recess of the add-on part and because of thebearing of the hollow profile under pre-stress as a consequence of themore extensive expansion, the add-on part obtains, at least at somepoints or in subregions of the recess walls of the add-on part, axialfixing and at the same time a rotationally fixed connection on thehollow profile. The non-releasable jamming of the add-on part to thehollow profile, the jamming being achieved in a simple manner merely byapplication of an internal high pressure in the hollow profile, requiresneither additional securing elements nor a high outlay on apparatus andfitting outlay. Since the reliability of the joining method is ensuredin the case of the material of the add-on part or holder, which materialis low in strength (has a low yield strength) and as a result virtuallydoes not spring back elastically after deformation, but rather is verysusceptible to fracturing during the deformation, the arrangement of therecess and spacing of it away from the end sides of the add-on part orholder, which end sides lie transversely with respect to thelongitudinal extent of the hollow profile or casing tube, ensure thatthe hollow profile material can flow into the recess without immediatelyresulting in an excessive contact stress acting in the radial preferreddirection between the hollow profile and the add-on part, which stresswould destroy the add-on part. The contact pressure of the hollowprofile against the add-on part, which pressure arises in the bearing inthe recess, is of a sufficient size to be able to transmit torsionalmoments within certain limits and therefore to achieve a sufficienttorsional rigidity of the joining connection, but in turn is not sogreat that the add-on part—as mentioned above—would be destroyed byexploding.

Furthermore, the two joining partners, e.g., the hollow profile andadd-on part, in the joining connection are, as a result of the joiningusing internal high pressure, coordinated with each other in a veryexact and reproducible manner in their relative axial and radialpositioning with respect to each other, with the result that the joiningconnection is virtually tolerance-free. This is of considerableimportance especially when considering the tolerances of the entireconstruction arrangement in which the joining connection is situated,for example, the steering column.

In order to compensate for the shortening of the hollow profile duringthe expansion, the length of the starting part has to be dimensioned tobe correspondingly larger in size. Moreover, the holder for the steeringcolumn switch in the steering column is merely representative of allpossible, conceivable holders on the steering column, for example, aholder for securing the steering column on the dashboard or on atransverse support.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features of the invention are evident from the dependent claims.Moreover, the invention is explained in greater detail below withreference to an exemplary embodiment illustrated in the drawings, inwhich:

FIG. 1 a shows, in a perspective view, a section of a tubular hollowprofile;

FIG. 1 b shows, in a perspective view, an add-on part of the joiningconnection according to the invention;

FIG. 2 shows, in a perspective view, a holder of the steering columnaccording to the invention;

FIG. 3 shows, in a lateral section, the add-on part from FIG. 1 b in aplug-in connection according to the principles of the invention togetherwith the hollow profile from FIG. 1 a before the internal high-pressuredeformation process; and

FIG. 4 shows, in a lateral section, the plug-in connection from FIG. 3after the internal high-pressure deformation process.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 a illustrates a circumferentially closed hollow profile 1 whichconsists of a ductile steel material, preferably of St 37 or St 52. FIG.1 b shows an add-on part 2 which enters into the joining connectionaccording to the invention together with the hollow profile 1. Theadd-on part 2 is of annular design and consists of a low-strengthcasting material, of a die casting or injection molding, preferably ofZnAL4Cul, or of a low-strength steel or of a light metal material. Thematerial is selected in such a manner that in each case it has a loweryield strength than that of the hollow profile 1. In this exemplaryembodiment, the add-on part 2 has, at one end, an annular flange 3, fromthe center of which an introductory stub 4 having a passage opening 5protrudes vertically. The annular flange 3 has two securing holes 6which lie diametrically opposite each other and via which the add-onpart 2, or after the joining process also the hollow profile 1, areattached to the periphery of the joining bond of hollow profile 1 andadd-on part 2—in a manner fixed on the bodywork in the event of thejoining bond being used in the body shell of a motor vehicle—or aresecured on the joining bond via the further components. A recess 10,which may be an annular freely turned recess, is formed on the inside 7of the passage opening 5, said recess being spaced away from the endsides 8, 9 of the add-on part 2, which end sides lie, in the sliding-fitposition, transversely with respect to the longitudinal direction of thehollow profile 1 which is to be inserted.

The hollow profile 1 may, for example, be a casing tube of a steeringcolumn of a motor vehicle, which tube surrounds the steering spindle ofthe steering column. The steering column has a plurality of holderswhich form the add-on parts 2. One of these holders can be seen in FIG.2, which holder, in a departure from the above-mentioned add-on part 2,does not have an annular flange 3, but rather consists of a ring 11which is to be approximately equivalent to the introductory stub 4 andat whose outer circumference a material tab 12 protrudes downwards. Thismaterial tab 12 is of tong-shaped design at its free end 13 and servesas a securing element for a steering column switch.

The production of the joining connection is further described inconnection with FIGS. 3 and 4. First, the selection of the materials ofthe joining partners hollow profile 1 and add-on part 2 is important. Inthis case, the hollow profile 1 consists of a ductile material which canbe reliably expanded during the subsequent internal high-pressuredeformation process. Most types of steel are conceivable for thispurpose. The hollow profile 1 may be drawn or rolled from a sheet blankand then welded along the longitudinal seam. From the aspect oflightweight construction, in the design of the add-on part 2, use isgenerally made of a material which has a lower yield strength than thematerial of the hollow profile 1. The add-on part 2 is generally of acomplicated design, depending on purpose and requirements, and so it isfavorable, from the point of view of cost and against the background ofa low outlay on mold and work, to cast or injection mold the add-on part2 as a light metal cast part having a discarded core. Similarly, it canbe formed by forging a lightweight steel.

In the case of production as a cast part, the recess 10 of the add-onpart 2 is cast at the same time or is incorporated, preferably freelyturned, in a subsequent machining process. If the add-on part 2 isforged, the recess 10 can subsequently be engraved, turned or milledout. The add-on part 2 is slid with its passage opening 5 onto thehollow profile 1 at the designated joining location, as shown in FIG. 3.

In the sliding-fit position reached, an expansion lance is then insertedinto the hollow profile 1, said expansion lance having an axial holewith a fluid high-pressure generating system connected at one end and infront of which, at the other end, there branches off at least one radialduct with a discharging hole on the outer circumference of the expansionlance. The discharging hole is surrounded by two annular seals which arespaced apart axially and are arranged on the expansion lance. Theexpansion lance is inserted into the hollow profile 1 sufficiently farsuch that the discharging hole lies at the location of the recess 10 ofthe add-on part 2 surrounding the hollow profile 1. A pressurized fluidis then conducted via the axial hole and the radial holes of theexpansion lance onto the inside of the hollow profile 1 which isexpanded locally there on account of the very high fluid pressure (>700bar) and because of its ductility.

The hollow profile material flows in this case into the recess 10 andcomes to lie on the walls 14 thereof. This may take place at some pointsor, as can be seen from FIG. 4, with complete, form-fitting bearing. Inboth cases, the add-on part 2 is fixed in an axially non-releasablemanner on the hollow profile 1 and is also held in a rotationally fixedmanner thereon on account of the frictional connection at the bearingpoints. This is optimal in the case of a complete form-fittingconnection, i.e., exact bearing of the hollow profile 1 against therecess walls 14 of the add-on part 2. In order to obtain the connectionin a simple manner and without a subsequent calibration step which mayimpair the material and is therefore not reliable, the recess 10 is ofcurved design with a shallow rise from its base 15 as far as its edges16 in accordance with the shaping characteristics of a free expansion ofthe hollow profile 1. The free expansion is distinguished in that thehollow profile 1 forms a bearing contact with the joining partner, theadd-on part 2, only at the end of the expansion.

In the present invention, the expansion of the hollow profile wall onthe hollow profile 1 by means of internal high pressure results in theformation of a locking element which bears over the entire surfaceagainst the recess walls 14 and jams the hollow profile 1 immovably tothe add-on part 2. In this exemplary embodiment, the locking element isformed by an annular bead 17 in accordance with the design of the recess10 as an annular groove. Otherwise, it is conceivable to form on theinside 7 one or more hollows distributed over the, circumferencethereof, in place of the annular groove. This has the advantage that theform-fitting connection achieved after the internal high-pressuredeformation is also effective in a radially directed fixing of theadd-on part 2 on the hollow profile 1, with the result that thefrictional connection in the locking plays only a subordinate role hereand, as a result, even higher torsional moments than in the precedingexemplary embodiment can be absorbed. A further improvement in thedurability of the joining connection with respect to mechanical loadscan be achieved by roughening the inside 7 of the add-on part 2 orholder, in which the wall material of the hollow profile 1, whichmaterial flows while being subjected to the internal high pressure, canthen become wedged with microprecision the locking element.

1. A joining connection comprising a circumferentially closed hollowprofile and an add-on part which defines a passage opening, and, on aninside of the passage opening, defines a recess which is spaced awayfrom end sides of the add-on part, wherein the add-on part is slid withthe passage opening onto the hollow profile and jammed to the hollowprofile in this sliding-fit position by an expansion of the hollowprofile, the expansion being formed by internal high-pressuredeformation, and further wherein the add-on part consists of a materialof lower yield strength than a material of the hollow profile, and theadd-on part is only jammed to the hollow profile locally at a locationof the recess.
 2. The joining connection according to claim 1, whereinthe recess is an annular freely turned recess.
 3. The joining connectionaccording to claim 1, wherein the hollow profile consists of a ductilesteel material, and the add-on part consists of one of a castingmaterial, a die casting and an injection molding, having alower-strength than the ductile steel or material.
 4. The joiningconnection according to claim 1, wherein the recess is of curved designwith a shallow rise extending from a base to opposing edges of therecess.
 5. The joining connection according to claim 1, wherein anexpanded point of the hollow profile bears in an exact manner against awall defining the recess.
 6. A method for producing a joining connectionbetween a circumferentially closed hollow profile and an add-on partwhich is provided with a passage opening, a recess which is spaced awayfrom end sides of the add-on part being formed on an inside of thepassage opening, comprising the steps of sliding the add-on part withits passage opening onto the hollow profile, and expanding the hollowprofile, in the sliding-fit position reached, by a fluidic internal highpressure delivered by an expansion lance inserted into the hollowprofile, in such a manner that the hollow profile is jammed immovably tothe add-on part, wherein the add-on part is comprised of a material oflower yield strength than a material of the hollow profile, and whereinthe hollow profile is only expanded into the recess locally.
 7. Themethod according to claim 6, wherein the recess is of curved design witha shallow rise from a base to opposing edges of the recess, and whereinthe hollow profile is expanded until it bears completely against a walldefining the recess.
 8. The method according to claim 6, wherein theadd-on part is cast as a cast part having a discarded core and whereinthe recess is cast at the same time as the add-on part.
 9. The methodaccording to claim 6, wherein the add-on part is injection molded or diecast and the recess is subsequently freely turned.
 10. The methodaccording to claim 6, wherein the add-on part is formed, in particularforged, from a low-strength steel, and wherein the recess is thenengraved, turned or milled out from the add-on part.
 11. A steeringcolumn of a motor vehicle comprising a casing tube which surrounds asteering spindle and forms a hollow profile, and a holder, constitutingan add-on part, for example for a steering column switch, the holderjoined onto the casing tube, wherein the holder, which consists of amaterial of lower yield strength than a material of the casing tube,defines a circumferentially closed passage opening and is slid onto thecasing tube, the passage opening having, on an inside, at least onerecess which is spaced away from end sides of the holder, which endsides lie transversely with respect to a longitudinal direction of thecasing tube, and wherein the casing tube has a locking element which, inthe sliding-fit position of the holder, is shaped radially from a wallof the holder locally at a location of the recess by a fluidic internalhigh pressure and is jammed in the recess as a consequence of a shape ofthe locking element, forming a non-releasable joining connection betweenthe holder and the casing tube.
 12. The steering column according toclaim 11, wherein the locking element bears over an entire surfaceagainst a wall defining the recess.
 13. The steering column according toclaim 11, wherein the recess is: formed by an annular groove and thelocking element is formed by an annular bead.
 14. The steering columnaccording to claim 11, wherein the casing tube consists of a ductilesteel material, and the holder consists of one of a casting material, aninjection molding and a die casting, having a lower-strength than theductile steel material.
 15. The steering column according to claim 11,wherein the recess is of curved design with a shallow rise from a baseto opposing edges of the recess.
 16. A joining connection comprising: acircumferentially closed hollow profile; and an add-on part defining apassage opening wherein an inside of the passage opening includes arecess which is spaced away from end sides of the add-on part; whereinthe circumferentially hollow profile is disposed within the passageopening of the add-on part and wherein the hollow profile is joined tothe add-on part by an expanded portion of the hollow profile, theexpanded portion of the hollow profile only received within the recessdefined by the add-on part; and further wherein the add-on part iscomprised of a material of lower yield strength than a material of thehollow profile.
 17. A method for producing a connection between acircumferentially closed hollow profile and an add-on part, the add-onpart defining a passage opening wherein an inside of the passage openingincludes a recess, comprising the steps of: disposing the hollow profilewithin the passage opening of the add-on part; and expanding the hollowprofile by a fluidic internal high pressure delivered by an expansionlance inserted into the hollow profile wherein the hollow profile isonly expanded into the recess, the recess spaced away from end sides ofthe add-on part; wherein the add-on part is comprised of a material oflower yield strength than a material of the hollow profile.
 18. Asteering column of a motor vehicle comprising: a casing tube forming ahollow profile; and a holder defining a circumferentially closed passageopening wherein an inside of the passage opening includes a recess whichis spaced away from end sides of the holder; wherein the casing tube isdisposed within the passage opening of the holder and locked in positionwithin the holder by a locking element of the casing tube that isreceived within the recess of the holder, the locking element of thecasing tube shaped radially by a wall of the holder defining the recessand a fluidic internal high pressure applied to the casing tube, theformed locking element jammed in the recess; and wherein the holder iscomprised of a material of lower yield strength than a material of thecasing tube.